The invention relates to an arrangement for supplying fuel to the fuel injectors mounted onto the cylinder heads of an internal combustion engine wherein fuel is supplied to the injectors by a pumping device through a pressure line under a static pressure.
Methods and fuel supply arrangements are known wherein fuel is pumped by a pump arrangement, which comprises at least one fuel pump, from a fuel tank through a pressure line under a certain pressure to the injectors of an internal combustion engine so as to be available for injection into the combustion chambers of the engine. A device for increasing the fuel injection pressure may be provided for improving the mixture formation by improving the atomization of the fuel spray during fuel injection. Particularly during the startup period of the internal combustion engine, a controllably dosed fuel amount can be provided for the first combustions in order to avoid fuel film depositions on the walls and to form a homogeneous fuel mixture, which can burn with relatively little emissions whereby the overall exhaust gas emissions from the engine can be reduced.
DE 101 27 516 A1 discloses a method, wherein, for the start-up period of the internal combustion engine, the fuel is supplied with a pressure of 45 bar to 55 bar. To this end, a fuel supply arrangement is provided wherein an engine-driven fuel pump generates a static injection pressure in a fuel line to which the injectors of the internal combustion engine are connected. Since during shut-down of the internal combustion engine, the high fuel pressure in the fuel supply line is disadvantageous, the pressure is released. In order to rapidly establish operating pressure upon engine startup thereby to improve the exhaust gas emissions, in the known fuel supply system, an additional electrically operated fuel pump is provided, which supplies fuel directly into the main fuel line and which is switched on during the engine start up procedure for providing the increased fuel pressure. DE 101 27 516 A1 proposes an arrangement with two serially arranged fuel pumps of different performance, wherein the fuel pumped by the first pump is fed by a high pressure pump into the fuel supply line. In this known arrangement, the mechanical drive of the fuel pumps can be disconnected from the engine drive by a switchable clutch and can be coupled to an electric drive in order to be able to utilize the high pressure pump for increasing the fuel pressure during the engine startup phase. This known arrangement requires substantial expenses in order to connect a device for increasing the fuel injection pressure since either a pump must be provided exclusively for the startup phase or in a staged pressure generation by means of a low-pressure and a high pressure pump, an expensive clutch or coupling arrangement must be provided for increasing the fuel injection pressure.
DE 100 05 589 A1 discloses a fuel supply arrangement wherein a pressure controller adjusts the injection pressure as needed by the internal combustion engine selectively to different pressure levels. Herein, in order to facilitate a safe hot start up of the internal combustion engine, the fuel pressure is increased for a short period in order to counteract vapor formation in the warm fuel. The arrangement provides for a fuel pressure of 3.5 bar for high fuel requirements and an increased pressure of 6 bar for hot startup operations which is generated by two serially arranged fuel pumps, each of which generates a pressure of 3 bar and which can be arranged in parallel or in series.
DE 199 39 051 A1 discloses a method using an additional fuel pump for generating the required high fuel pressure during the engine startup phase. The additional fuel pump is electrically operated and electrically switchable and supplies fuel directly into the pressure line, so that, during the startup phase in which the mechanically operated pump cannot yet supply the required high pressure level in the pressure line, an essentially higher pressure is available. The additional electric pump is arranged in parallel with the mechanical pump and is also operated during normal engine operation so as to contribute to providing a high fuel pressure.
DE 195 39 885 A1 discloses a method of operating an internal combustion engine and a fuel supply arrangement wherein a first electrically operated displacement pump supplies fuel to a mechanical engine-driven high pressure pump. The displacement pump in this case is to pump more fuel than is required and excess fuel is returned to the tank via a return line. The supply pressure generated is further increased by the high pressure pump so as to provide in the pressure line the required injection pressure. In order to counter the problem of the vapor formation in the fuel lines when, with the internal combustion engine shut down, the pressure in the fuel line drops, the known arrangement interrupts in the startup phase of the engine the return flow of the electric low pressure pump so that the electric displacement pump generates an increased pressure by which the fuel lines are flushed and any steam bubbles are pushed out of the lines. The arrangement does not provide for an increase of the fuel pressure when needed for improved atomizing of the injected fuel jet under certain operating conditions beyond the normal operating level.
It is the object of the present invention to provide, with the least possible expenditure, a fuel supply arrangement with which, without limitations for the normal operation, the fuel injection pressure can be increased during the start-up phase of the internal combustion engine and the fuel injection volume can be accurately controlled.